\begin{tikzpicture}
    % 由各圆两两相切，得： (R - r)^2 + (R/2)^2 = (R/2 + r)^2
    % 解得: r = R/3

    % 大圆
    \pgfmathsetmacro{\R}{3}
    \tkzDefPoints{0/0/A, \R/0/O, 2*\R/0/B}
    \tkzDrawSegment[thick](A,B)
    \tkzDrawArc[very thick](O,B)(A)
    \tkzDrawPoint(O)

    % 左侧的小圆 A
    \tkzDefPoints{0.5*\R/0/O_1}
    \tkzDrawArc[very thick](O_1,O)(A)
    \tkzDrawPoint(O_1)

    % 右侧的小圆 B
    \tkzDefPoints{1.5*\R/0/O_2}
    \tkzDrawArc[very thick](O_2,B)(O)
    \tkzDrawPoint(O_2)

    % 上方的小圆 C
    \pgfmathsetmacro{\r}{\R/3}
    \tkzDefPoints{\R/\R-\r/O_3, \R/\R/C}
    \tkzDrawCircle[very thick](O_3,C)
    \tkzDrawPoint(O_3)
\end{tikzpicture}
